1. Field of the invention
The invention relates to an imaging electron-optical apparatus, e.g. photo-electron emission microscope, in which a final electron image produced by an electron-optical imaging system of the apparatus is intensified by an electron multiplier.
2. Description of the Related Art
Image amplifiers are used in numerous electron-optical apparatus. Typical examples are photo-electron emission microscopes and reflection microscopes of the Bauer and Telieps type. The latter type of apparatus is known as "LOW ENERGY ELECTRON REFLECTION MICROSCOPE", dubbed LEERM OR LEEM in scientific publications (W. Telieps and E. Bauer, Ultramicroscopy 17 (1985) 57).
An effective and low-cost solution of the image intensifier problem is the channel-plate electron multiplier (in short, "channel plate"), which is directly exposed to the electron pattern that represents the final image produced in the imaging electron-optical apparatus. This is specifically true when large image areas, i.e. a large number of picture elements or pixels, are to be amplified or intensified. A channel-plate image intensifier generally comprises at least one channel-plate followed by a transparent luminescent screen which is positioned in close proximity parallel to an output surface of the channel-plate. The electron pattern amplified within the channels of the channel-plate(s) is accelerated onto the luminescent screen and simultaneously approximately focussed so that a visible optical image is produced by the impinging electrons.
The use of channel-plate image intensifiers in such imaging electron optical apparatus as photo-electron emission microscopes and reflection microscopes is known ( see e.g. B. P. Tonner et al., Rev. Sci. Instrum. 59 (1988) 853 and the above mentioned paper by Telieps et al.).